Hydrothermally stable, low-temperature nox reduction nh3-scr catalyst

ABSTRACT

A catalyst composition includes a heterobimetallic zeolite characterized by a chabazite structure loaded with copper ions and at least one trivalent metal ion other than Al 3+ . The catalyst composition decreases NO x  emissions in diesel exhaust and is suitable for operation in a catalytic converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/404,071, filed on Feb. 24, 2012, which is herein incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The United States Government has rights in this invention pursuant tocontract no. DE-AC05-00OR22725 between the United States Department ofEnergy and UT-Battelle, LLC.

BACKGROUND OF THE INVENTION

Diesel engines are known to be significantly more fuel efficient thantheir gasoline counterparts. Therefore, the introduction of dieselengine in on-road and off-road systems (e.g., industrial or householdequipment, such as heavy machinery and lawnmowers) is highly desirable.Furthermore, the gasoline engines, operating in oxygen rich environment(lean gasoline engines) are also more fuel efficient than currently usedstoichiometric engines.

The high fuel efficiency of diesel engines and lean gasoline enginesresults in oxygen-rich (i.e., “lean”) exhaust that primarily containsNO_(x) gases. Although NO_(x) gases can be efficiently removed fromoxygen-poor exhausts, as produced in gasoline engine emissions, theremoval of NO_(x) gases in diesel/lean gasoline engine lean emissionscontinues to be a significant challenge. In particular, the standardthree-way catalyst works well for gasoline engines but does not meet EPAregulatory requirements when used for diesel engines.

In order to meet EPA regulatory requirements for diesel engines,extensive efforts are under way to find catalysts that can effectivelytreat NO_(x) in the oxygen-rich emissions emitted by diesel engines. Theleading approach for reduction of NO_(x) in diesel emissions isselective catalytic reduction (SCR). In SCR, ammonia or urea is oftenemployed as a reductant. The best known NH₃-SCR catalysts for NO_(x)reduction under the lean environment of diesel engine emissions areCu-ZSM-5 and Fe-ZSM-5. These have been shown to function effectivelyonly within narrow temperature ranges. Cu-ZSM-5 generally exhibits abetter NO_(x) reduction activity at lower temperatures while Fe-ZSM-5exhibits better activity at higher temperatures. Thus, a combination ofCu-ZSM-5 and Fe-ZSM-5 zeolites (i.e., as a heterogeneous mixture) hasbeen used in an effort to effectively treat NO_(x) within a broadenedtemperature range. The most recent generation NH₃-SCR catalyst is basedon Cu-SSZ-13 and is now commercially available.

Although the Cu/Fe mixtures provide an improvement in emissionsprocessing for diesel-operated passenger vehicles, the Cu/Fe mixtures issignificantly inadequate at low temperatures. In particular, thecatalysts currently employed do not efficiently reduce NO_(x) emissionsat low temperatures, such as 150-200° C., which is more critical inoff-road diesel engines than in passenger vehicles. Moreover, the Cu/Femixture may be adequately efficient only within separate narrowtemperature ranges, e.g., a high and a low temperature range. However,particularly for off-road diesel engines that can operate under a broadrange of temperatures, there would be a significant benefit in acatalyst that can operate efficiently under a wide range of temperatures(for example, from 150° C. to 650° C.). If a gasoline engine is operatedin lean mode, not much NO_(x) is produced at low temperature. However,the catalyst described in this invention is suitable for use withgasoline engines operating in lean mode as well as diesel engines usedfor transportation (cars, trucks, railroad engines, ships, etc.)

BRIEF SUMMARY OF THE INVENTION

In accordance with examples of the present invention, the foregoing andother objects are achieved by a catalyst composition that includes aheterobimetallic zeolite characterized by a chabazite structure loadedwith copper ions and at least one trivalent metal ion other than Al³⁺.The catalyst composition decreases NO_(x) emissions in diesel exhaustand is suitable for operation in a catalytic converter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing comparative performance of CuFe-SSZ-13 andCu-SSZ-13 catalysts in accordance with examples of the presentinvention.

FIG. 2 is a graph showing comparative performance of CuFe-SSZ-13 andaged CuFe-SSZ-13 catalysts in accordance with examples of the presentinvention.

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a catalyst for mitigating (i.e.,removing or reducing) NO_(x) emissions from hydrocarbon (for example,diesel, gasoline and/or kerosene exhaust). The catalyst includes a newclass of heterobimetallic zeolites based on chabazite structure, such asCuFe-SSZ-13, for example. The new zeolites described herein overcome thehydrothermal durability issues of all known NH₃-SCR catalysts for NO_(x)reduction while preserving their high NO_(x) reduction capability at lowtemperatures.

The zeolite considered herein can be any of the porous aluminosilicatestructures known in the art that are stable under high temperatureconditions, i.e., of at least 100° C., 150° C., 200° C., 250° C., 300°C., and higher temperatures up to, for example, 500° C., 550° C., 600°C., 650° C., 700° C., 750° C., 800° C., 850° C., or 900° C. Inparticular examples of the present invention, the zeolite is stable fromat least 100° C. and up to 700° C. Typically, the zeolite is ordered byhaving a crystalline or partly crystalline structure. The zeolite cangenerally be described as a three-dimensional framework containingsilicate (SiO₂ or SiO₄) and aluminate (Al₂O₃ or AlO₄) units that areinterconnected (i.e., cross-linked) by the sharing of oxygen atoms.

The zeolite can be microporous (i.e., pore size of less than 2 μm),mesoporous (i.e., pore size within 2-50 μm, or sub-range therein), or acombination thereof. In several examples of the present invention, thezeolite material is completely or substantially microporous. By beingcompletely or substantially microporous, the pore volume due tomicropores can be, for example, 100%, or at least 95%, 96%, 97%, 98%,99%, or 99.5%, with the remaining pore volume being due to mesopores, orin some examples of the present invention, macropores (pore size greaterthan 50 um). In other examples of the present invention, the zeolitematerial is completely or substantially mesoporous. By being completelyor substantially mesoporous, the pore volume due to mesopores can be,for example, 100%, or at least 95%, 96%, 97%, 98%, 99%, or 99.5%, withthe remaining pore volume being due to micropores, or in some examplesof the present invention, macropores. In yet other examples of thepresent invention, the zeolite material contains an abundance of bothmicropores and mesopores. By containing an abundance of both microporesand mesopores, the pore volume due to mesopores can be, for example, upto, at least, or precisely 50%, 60%, 70%, 80%, or 90%, with the porevolume balance being due to mesopores, or vice-versa.

The various forms of zeolite are commonly known by respectiveabbreviations such as, for example, ABW, ACO, AEI, AEN, AFG, AFN, AFT,AFX, APC, APD, ATN, ATT, ATV, AWO, AWW, BCT, BIK, BOF, BRE, CAS, CDO,CHA, DFT, DOH, EAB, EPI, ERI, ESV, FAR, FRA, GIS, GIU, IHW, ITE, ITW,JBW, JRY, KFI, LAU, LEV, LIO, LOS, LTA, LTN, MAR, MON, MTF, MWW, NAT,NSI, OWE, PAU, PHI, RHO, RTE, RTH, RWR, SAS, SAT, SAV, SBN, SW, SOD,STI, STT, THO, TOL, UEI, UFI, or ZON. Some particular examples ofzeolites include the chabazite class of zeolites (for example, SSZ-13,SSZ-62, Phi, SAPO-34, LZ-218, and Linde D). The compositions,structures, and properties of chabazite zeolites are well-known in theart, and have been described in detail, as found in, for example, U.S.Pat. Nos. 4,544,538, 6,709,644, 4,124,686, 4,333,859, and 2,950,952, thecontents of which are incorporated herein by reference in theirentirety.

The zeolite can have any suitable silica-to-alumina (i.e., SiO₂/Al₂O₃ or“Si/Al”) ratio. For example, in various examples of the presentinvention, the zeolite can have a Si/Al ratio of precisely, at least,less than, or up to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100,120, 150, or 200, or a Si/Al ratio within a range bounded by any two ofthe foregoing values. In particular examples of the present invention,the zeolite possesses a Si/Al ratio of 1 to 45.

In particular examples of the present invention, the zeolite is SSZ-13,which belongs to the ABC-6 family of zeolites, all of which are alsoconsidered herein. In particular examples of the present invention, theSSZ-13 zeolite is represented by the formula RN_(a)Na_(b)Al_(2.4)Si_(33.6)O₇₂.wH₂O (1.4<a<27)(0.7<b<4.3)(1<w<7), where RN isN,N,N-1-trimethyladamantammonium.

Typically, the zeolite contains an amount of cationic species. As iswell known in the art, the amount of cationic species is generallyproportional to the amount of aluminum in the zeolite. This is becausethe replacement of silicon atoms with lower valent aluminum atomsnecessitates the presence of countercations to establish a chargebalance. Some examples of cationic species include hydrogen ions (H⁺),alkali metal ions, alkaline earth metal ions, and main group metal ions.Some examples of alkali metal ions that may be included in the zeoliteinclude lithium (Li⁺), sodium (Na⁺), potassium (K⁺), rubidium (Rb⁺), andcesium (Cs⁺). Some examples of alkaline earth metal ions that may beincluded in the zeolite include (Be²⁺), magnesium (Mg²⁺), calcium(Ca²⁺), strontium (Sr²⁺), and barium (Ba²⁺). Some examples of main groupmetal ions that may be included in the zeolite include boron (B³⁺),gallium (Ga³⁺), indium (In³⁺), and arsenic (As³⁺). In some examples ofthe present invention, a combination of cationic species is included.The cationic species can be in a trace amount (e.g., no more than 0.01or 0.001%), or alternatively, in a significant amount (e.g., above0.01%, and up to, for example, 0.1, 0.5, 1, 2, 3, 4, or 5% by weight ofthe zeolite).

The zeolite described above is loaded with an amount of copper ions. Thecopper ions can be cuprous (Cu⁺) or cupric (Cu²⁺) in nature. The copperloading can be any suitable amount. In different examples of the presentinvention, the copper loading is precisely, at least, less than, or upto, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%,0.09%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%,2.1%, 2.2%, 2.3%, 2.4%, or 2.5%, or a copper loading within a rangebounded by any two of the foregoing values, wherein the loading isexpressed as the amount of metal by weight of the zeolite. In particularexamples of the present invention, the copper loading is any value up to2.5%.

In addition to copper ions, the zeolite catalyst of the instantinvention also includes at least one trivalent metal ion. As usedherein, the term “trivalent metal ion” is defined as a trivalent metalion other than aluminum (Al³⁺). Without wishing to be bound by anytheory, it is believed that the trivalent metal is incorporated into thezeolite material. Thus, the incorporated trivalent metal ion is believedto be bound in the zeolite to an appropriate number of oxygen atoms,i.e., as a metal oxide unit in close proximity (e.g., within electroniccontact or communication) to the copper ions. The close proximitybetween the trivalent metal ions and copper ions is believed to cause acombined effect different than the cumulative effect of these ions whenthey are not in such close proximity. The effect primarily consideredherein is the effect on the resulting catalyst's ability to processNO_(x) gases (i.e., the catalyst's NO_(x) conversion ability).

In some examples of the present invention, only one type of trivalentmetal ion aside from aluminum is incorporated into the zeolite. In otherexamples of the present invention, at least two types of trivalent metalions aside from aluminum are incorporated into the zeolite. In yet otherexamples of the present invention, at least three types of trivalentmetal ions aside from aluminum are incorporated into the zeolite. In yetother examples of the present invention, precisely two or preciselythree types of trivalent metal ions aside from aluminum are incorporatedinto the zeolite.

Each of the trivalent metal ions can be included in any suitable amount,such as, precisely, at least, less than, or up to, for example, 0.01%,0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 1.0%, 1.1%,1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%,2.4%, or 2.5%, or an amount within a range bounded by any two of theforegoing values. In particular examples of the present invention, eachof the trivalent metal ions can be included in an amount of, precisely,at least, less than, or up to 2.5%. In examples of the present inventionwhere more than one type of trivalent metal ion is included, the loadingof each metal can be independently selected from any of the aboveexemplary amounts or ranges therein. In other examples of the presentinvention, the total amount of trivalent metal ions other than aluminumconforms to any of the exemplary values provided above.

In a first set of examples of the present invention, at least onetrivalent metal ion is selected from trivalent transition metal ions.The one or more transition metals can be selected from any or a selectportion of the following types of transition metals: elements of GroupsIIIB (Sc group), IVB (Ti group), VB (V group), VIB (Cr group), VIIB (Mngroup), VIIIB (Fe and Co groups) of the Periodic Table of the Elements.Some examples of trivalent transition metal ions include Sc³⁺, Y³⁺, V³⁺,Nb³⁺, Cr³⁺, Fe³⁺, and Co³⁺. In other examples of the present invention,the trivalent metal ion excludes all transition metal ions, oralternatively, excludes any one, two, or more classes or specificexamples of transition metal ions provided above. In particular examplesof the present invention, the trivalent transition metal ions includeSc³⁺, or Fe³⁺, or a combination thereof.

In a second set of examples of the present invention, at least onetrivalent metal ion is selected from trivalent main group metal ions.The one or more main group metals can be selected from any or a selectportion of elements of Group IIIA (B group) and/or Group VA (N group) ofthe Periodic Table, other than aluminum. Some examples of trivalent maingroup metal ions include Ga³⁺, In³⁺, As³⁺, Sb³⁺, and Bi³⁺. In otherexamples of the present invention, the trivalent metal ion excludes allmain group metal ions other than aluminum, or alternatively, excludesany one, two, or more classes or specific examples of main group metalions provided above. In particular examples of the present invention,the trivalent main group metal ions include at least In³⁺.

In a third set of examples of the present invention, at least onetrivalent metal ion is selected from trivalent lanthanide metal ions.Some examples of trivalent lanthanide metal ions considered hereininclude La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺,Er³⁺, Tm³⁺, Yb³⁺, and Lu³⁺. In particular examples of the presentinvention, the trivalent lanthanide metal ion is selected from one or acombination of La³⁺, Ce³⁺, Pr³⁺, and Nd³⁺. In further particularexamples of the present invention, the trivalent lanthanide metal ion isor includes La³⁺.

In a fourth set of examples of the present invention, at least twotrivalent metal ions are selected from trivalent transition metal ions.Some combinations of trivalent transition metal ions considered hereininclude Sc³⁺ in combination with one or more other trivalent transitionmetal ions, or Fe³⁺ in combination with one or more other trivalenttransition metal ions, or Y³⁺ in combination with one or more othertrivalent transition metal ions.

In a fifth set of examples of the present invention, at least twotrivalent metal ions are selected from trivalent main group metal ions.Some combinations of trivalent main group metal ions considered hereininclude In³⁺ in combination with one or more other trivalent main groupmetal ions, or Ga³⁺ in combination with one or more other trivalent maingroup metal ions, or As³⁺ in combination with one or more othertrivalent main group metal ions.

In a sixth set of examples of the present invention, at least twotrivalent metal ions are selected from trivalent lanthanide metal ions.Some combinations of trivalent lanthanide metal ions considered hereininclude La³⁺ in combination with one or more other trivalent lanthanidemetal ions, or Ce³⁺ in combination with one or more other trivalentlanthanide metal ions, or Pr³⁺ in combination with one or more othertrivalent lanthanide metal ions, or Nd³⁺ in combination with one or moreother trivalent lanthanide metal ions.

In a seventh set of examples of the present invention, at least onetrivalent metal ion is a trivalent transition metal ion and at least onetrivalent metal ion is a trivalent lanthanide metal ion. For example, inparticular examples of the present invention, at least one trivalentmetal ion is selected from Sc³⁺, Fe³⁺, and/or Y³⁺, and another trivalentmetal ion is selected from La³⁺, Ce³⁺, Pr³⁺, and/or Nd³⁺.

In an eighth set of examples of the present invention, at least onetrivalent metal ion is a trivalent transition metal ion and at least onetrivalent metal ion is a trivalent main group metal ion. For example, inparticular examples of the present invention, at least one trivalentmetal ion is selected from Sc³⁺, Fe³⁺, and/or Y³⁺, and another trivalentmetal ion is selected from In³⁺, Ga³⁺, and/or In³⁺.

In a ninth set of examples of the present invention, at least onetrivalent metal ion is a trivalent main group metal ion and at least onetrivalent metal ion is a trivalent lanthanide metal ion. For example, inparticular examples of the present invention, at least one trivalentmetal ion is selected from Sc³⁺, Fe³⁺, and/or Y³⁺, and another trivalentmetal ion is selected from La³⁺, Ce³⁺, Pr³⁺, and/or Nd³⁺.

In a tenth set of examples of the present invention, at least threetrivalent metal ions are included in the zeolite. The at least threetrivalent metal ions can be selected from trivalent transition metalions, trivalent main group metal ions, and/or trivalent lanthanide metalions.

In particular examples of the present invention, one, two, three, ormore trivalent metal ions are selected from Sc³⁺, Fe³⁺, Y³⁺, La³⁺, Ce³⁺,Pr³⁺, Nd³⁺, In³⁺, and/or Ga³⁺. In more particular examples of thepresent invention, one, two, three, or more trivalent metal ions areselected from Sc³⁺, Fe³⁺, La³⁺, and/or In³⁺.

The zeolite catalyst described above is typically not coated with ametal-containing film or layer. However, the instant invention alsocontemplates the zeolite catalyst described above coated with ametal-containing film or layer as long as the film or layer does notsubstantially impede the catalyst from effectively functioning as aNO_(x) reduction catalyst as intended herein. By being coated, the filmor layer resides on the surface of the zeolite. In some examples of thepresent invention, the surface of the zeolite refers to only the outersurface (i.e., as defined by the outer contour area of the zeolitecatalyst), while in other examples of the present invention, the surfaceof the zeolite refers to or includes inner surfaces of the zeolite, suchas the surfaces within pores or channels of the zeolite. Themetal-containing film or layer can serve, for example, to adjust thephysical characteristics of the catalyst, the catalytic efficiency, orcatalytic selectivity. Some examples of metal-containing surfacesinclude the oxides and/or sulfides of the alkali metals, alkaline earthmetals, divalent transition or main group metals (e.g., Zn²⁺, Fe²⁺,Co²⁺, Ni²⁺, Pd²⁺, Pt²⁺, Sn²⁺, or Pb²⁺), tetravalent transition metals(e.g., Ti⁴⁺, Zr⁴⁺, Rh⁴⁺, Ir⁴⁺, Mn⁴⁺, Ge⁴⁺, Sn⁴⁺, and Te⁴⁺), pentavalenttransition or main group metals (e.g., Nb⁵⁺, Ta⁵⁺, and Sb⁵⁺), andhexavalent transition metals (e.g., Cr⁶⁺, Mo⁶⁺, and W⁶⁺). In otherexamples of the present invention, one or more classes or specific typesof any of the above additional metal ions are excluded from the zeolitecatalyst.

The catalyst described herein can be synthesized by any suitable methodknown in the art. The method considered herein should incorporate themetal ions (i.e., copper and one or more trivalent metal ions)homogeneously into the zeolite. The resulting metal-loaded catalystcontains a homogeneous distribution of the metal ions on a molecularlevel, i.e., the catalyst does not contain macroscopic regionscontaining only one type of metal ion, as would be obtained by grindingand mixing of two zeolite sources that each contain a different metalion.

In particular examples of the present invention, the catalyst describedherein is prepared by, first, impregnating the zeolite with the metalsto be loaded. The impregnating step can be achieved by, for example,treating the zeolite with one or more solutions containing the metals tobe loaded. By treating the zeolite with the metal-containing solution,the metal-containing solution is contacted with the zeolite such thatthe solution is absorbed into the zeolite, preferably into the entirevolume of the zeolite.

In one embodiment, the impregnating step is achieved by treating thezeolite with a solution that contains all of the metals to be loaded. Inanother embodiment, the impregnating step is achieved by treating thezeolite with two or more solutions, wherein the different solutionscontain different metals or combinations of metals. Each treatment ofthe zeolite with an impregnating solution corresponds to a separateimpregnating step. Typically, when more than one impregnating step isemployed, a drying and/or thermal treatment step is employed between theimpregnating steps.

The metal-impregnating solution contains at least one or more metal ionsto be loaded into the zeolite, as well as a liquid carrier fordistributing the metal ions into the zeolite. The metal ions aregenerally in the form of metal salts. Preferably, the metal salts arecompletely dissolved in the liquid carrier. The metal salt contains oneor more metal ions in ionic association with one or more counteranions.Any one or more of the metal ions described above can serve as the metalion portion. The counteranion can be selected from, for example, halides(F⁻, Cl⁻, Br⁻, or I⁻), carboxylates (e.g., formate, acetate, propionate,or butyrate), sulfate, nitrate, phosphate, chlorate, bromate, iodate,hydroxide, β-diketonate (e.g., acetylacetonate), and dicarboxylates(e.g., oxalate, malonate, or succinate). In some examples of the presentinvention, the counteranion may contain one or more metals, includingone or more metals to be loaded into the zeolite. Some examples of suchcounter-anions include titanate, zirconate, vanadate, niobate,tantalate, chromate, molybdate, tungstate, arsenate, antimonate,stannate, and tellurate. In other examples of the present invention, oneor more classes or specific types of any of the foregoing counter-anionsare excluded from the impregnating solution (or alternatively, excludedfrom being incorporated into the zeolite).

In particular examples of the present invention, the catalyst isprepared by forming a slurry containing zeolite powder and the metals tobe incorporated. The resulting slurry is dried and fired to form apowder. The powder is then combined with organic and/or inorganicbinders and wet-mixed to form a paste. The resulting paste can be formedinto any desired shape, e.g., by extrusion into rod, honeycomb, orpinwheel structures. The extruded structures are then dried and fired toform the final catalyst. In other examples of the present invention, thezeolite powder, metals, and binders are all combined together to form apaste, which is then extruded and fired.

After impregnating the zeolite, the metal-loaded zeolite is typicallydried and/or subjected to a thermal treatment step (e.g., a firing orcalcination step). The thermal treatment step functions to permanentlyincorporate the impregnated metals into the zeolite, e.g., by formingmetal-oxide bonds within the zeolite material. In different examples ofthe present invention, the thermal treatment step can be conducted at atemperature of at least 100° C., 150° C., 200° C., 250° C., 300° C.,350° C., 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., 700° C.,750° C., or 800° C., or within a range therein, for a time period of,for example, 15 minutes, 30 minutes, 1 hour, 2 hours, 6 hours, 12 hours,24 hours, 30 hours, 36 hours, or 48 hours, or within a range therein. Inparticular examples of the present invention, the thermal treatment stepis conducted at a temperature of at least 500° C. for a time period ofat least two hours. In some examples of the present invention, thethermal treatment step includes a temperature ramping step from a lowertemperature to a higher temperature, and/or from a higher temperature toa lower temperature. For example, the thermal treatment step can includea ramp stage from 100° C. to 700° C., or vice-versa, at a rate of 1, 2,5, or 10° C./min.

Generally, the one or more heat treatment steps are conducted undernormal atmospheric pressure. However, in some examples of the presentinvention, an elevated pressure (e.g., above 1 atm and up to 2, 5, or 10atm) is employed, while in other examples of the present invention, areduced pressure (e.g., below 1, 0.5, or 0.2 atm) is employed.Furthermore, although the heat treatment steps are generally conductedunder a normal air atmosphere, in some examples of the presentinvention, an elevated oxygen, reduced oxygen, or inert atmosphere isused. Some gases that can be included in the processing atmosphereinclude, for example, oxygen, nitrogen, helium, argon, carbon dioxide,and mixtures thereof.

Generally, the zeolite catalyst described herein is in the form of apowder. In a first set of examples of the present invention, at least aportion, or all, of the particles of the powder have a size less than amicron (i.e., nanosized particles). The nanosized particles can have aparticle size of precisely, at least, up to, or less than, for example,1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300,350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, or 950nanometers (nm), or a particle size within a range bounded by any two ofthe foregoing values. In a second set of examples of the presentinvention, at least a portion, or all, of the particles of the powderhave a size at or above 1 micron in size. The micron-sized particles canhave a particle size of precisely, at least, up to, or less than, forexample, 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 microns(μm), or a particle size within a range bounded by any two of theforegoing values. In some examples of the present invention, singlecrystals or grains of the catalyst correspond to any of the sizesprovided above, while in other examples of the present invention,crystals or grains of the catalyst are agglomerated to provideagglomerated crystallites or grains having any of the above exemplarydimensions.

In other examples of the present invention, the zeolite catalyst can bein the form of a film, a coating, or a multiplicity of films orcoatings. The thickness of the coatings or multiplicity of coatings canbe, for example, 1, 2, 5, 10, 50, or 100 microns, or a range therein, orup to 100 micron thickness. In yet other examples of the presentinvention, the zeolite catalyst is in the form of a non-particulate(i.e., continuous) bulk solid. In still other examples of the presentinvention, the zeolite catalyst can be fibrous or in the form of a mesh.

The catalyst can also be mixed with or affixed onto a support materialsuitable for operation in a catalytic converter. The support materialcan be a powder (e.g., having any of the above particle sizes), granular(e.g., 0.5 mm or greater particle size), a bulk material, such as ahoneycomb monolith of the flow-through type, a plate or multi-platestructure, or corrugated metal sheets. If a honeycomb structure is used,the honeycomb structure can contain any suitable density of cells. Forexample, the honeycomb structure can contain 100, 200, 300, 400, 500,600, 700, 800, or 900 cells/in² (or from 62-140 cells/cm²) or greater.The support material is generally constructed of a refractorycomposition, such as those containing cordierite, mullite, alumina(e.g., α-, γ-, or θ-alumina), or zirconia, or a combination thereof.Honeycomb structures, in particular, are described in detail in, forexample, U.S. Pat. Nos. 5,314,665, 7,442,425, and 7,438,868, thecontents of which are incorporated herein by reference in theirentirety. When corrugated or other types of metal sheets are used, thesecan be layered on top of each other with catalyst material supported onthe sheets such that passages remain that allow the flow of exhaust gasbetween the sheets. The layered sheets can also be formed into astructure, such as a cylinder, by winding the sheets.

The catalyst described herein preferably exhibits a NO_(x) conversiontemperature profile that is improved over that of Cu-SSZ-13, asdescribed in U.S. Pat. No. 7,601,662.

In a first set of examples of the present invention, the catalystdescribed herein preferably exhibits a high NO_(x) conversion at 150° C.As used herein, the phrase “high NO_(x) conversion at 150° C.” isdefined as a NO_(x) conversion of at least or above 50%, 55%, 60%, 65%,70%, 75%, 80%, or 85% at 150° C.

In a second set of examples of the present invention, the catalystdescribed herein preferably exhibits a high NO_(x) conversion at 200° C.As used herein, the phrase “high NO_(x) conversion at 200° C.” isdefined as a NO_(x) conversion of at least or above 80%, 85%, or 90% at200° C.

In a third set of examples of the present invention, the catalystdescribed herein preferably exhibits a high NO_(x) conversion at atemperature in the range of 250° C. to 450° C. As used herein, thephrase “high NO_(x) conversion at 250-450° C.” is defined as a NO_(x)conversion of at least or above 60%, 65%, 70%, 75%, 80%, 85%, or 90% ata temperature of 250° C., 300° C., 350° C., 400° C., or 450° C., at atemperature in the range of 250° C. to 450° C., or temperatures thatvary within the range.

In a fourth set of examples of the present invention, the catalystdescribed herein preferably exhibits a high NO_(x) conversion at atemperature in the range of 500° C. to 525° C. As used herein, thephrase “high NO_(x) conversion at 500-525° C.” is defined as a NO_(x)conversion of at least or above 60%, 65%, 70%, 75%, 80%, or 85% at atemperature in the range of 500° C. to 525° C., or temperatures thatvary within the range.

In a fifth set of examples of the present invention, the catalystdescribed herein preferably exhibits a high NO_(x) conversion at atemperature of 550° C. As used herein, the phrase “high NO_(x)conversion at 550° C.” is defined as a NO_(x) conversion of at least orabove 60%, 65%, 70%, 75%, or 80% at a temperature of 550° C.

In a sixth set of examples of the present invention, the catalystdescribed herein preferably exhibits a high NO_(x) conversion at atemperature in the range of 600° C. to 650° C. As used herein, thephrase “high NO_(x) conversion at 600-650° C.” is defined as a NO_(x)conversion of at least or above 60%, 65%, 70%, 75%, or 80% at atemperature in the range of 600° C. to 650° C., or temperatures thatvary within the range.

In a seventh set of examples of the present invention, the catalystdescribed herein preferably exhibits a high NO_(x) conversion at 150° C.while also exhibiting a high NO_(x) conversion at 200° C., and/or a highNO_(x) conversion at 250-450° C., and/or a high NO_(x) conversion at500-525° C., and/or a high NO_(x) conversion at 550° C., and/or a highNO_(x) conversion at 600-650° C.

In some examples, the invention is directed to a catalytic converterthat contains therein as a catalyst the above-described metal-loadedzeolite catalyst. The catalyst is typically disposed on a refractorysupporting element, such as corrugated metal sheets or a honeycombstructure, as described above. The catalytic converter can be any of thecatalytic converters known in the art, and particularly, those catalyticconverters particularly suited for processing diesel fuel exhaust. Theconstruction and operation of such catalytic converters are well knownin the art, as described in detail in, for example, U.S. Pat. Nos.7,691,340, 7,678,348, 7,575,727, 7,442,425, 7,438,868, 7,412,824,7,288,230, 6,919,052, and 5,314,665, the contents of which are allherein incorporated by reference in their entirety.

As basic elements, the catalytic converter typically contains thecatalyst disposed on a supporting element such that passages are madeavailable for exhaust to pass therethrough, and the supported catalystenclosed in a metal casing. The metal casing is generally connected withone or more inlets (i.e., pipes) for transferring exhaust gases into thesupported catalyst. The metal casing may also include one or moregaskets.

In particular examples of the present invention, the catalytic converteris connected with a source of ammonia in order for ammonia to mix inwith the stream of exhaust gas. As is well known in the art, the ammoniafunctions as a reductant in selective catalytic reduction (SCR)processes. The ammonia can be in any suitable form, such as anhydrousammonia, aqueous ammonia, urea, ammonium carbonate, ammonium formate, orammonium carbamate. In some examples of the present invention, theammonia source is supplied continuously into the exhaust stream beforeand/or during the time the exhaust stream reaches the catalyst. In otherexamples of the present invention, the ammonia is suppliedintermittently. In other examples of the present invention, the ammoniasource is supplied before the exhaust stream reaches the catalyst. Inthis way, the ammonia source is first absorbed into the catalyst beforereacting with the exhaust stream. Generally, an ammonia storage tank isused to contain the ammonia source.

In designing a SCR system, numerous other elements can be interconnectedwith the catalytic converter and ammonia source. For example, avaporizer can be included between the ammonia source and catalyticconverter for converting (i.e., decomposing) the ammonia source intoammonia gas. A mixer may also be incorporated between the ammonia sourceand catalytic converter (or between vaporizer and catalytic converter)to mix ammonia with the exhaust stream. Other elements, such as heaters,pumps, and fans, can be included in order to optimize the system. TheSCR system can be integrated into any system that makes use of a leanburn engine, particularly those engines that use diesel fuel. The SCRsystem can be integrated into, for example, the engine system of apassenger vehicle, truck, utility boiler, industrial boiler, solid wasteboiler (i.e., as used in the processing of municipal waste), ship,locomotive, tunnel boring machine, submarine, construction equipment,gas turbine, power plant, airplane, lawnmower, or chainsaw.

Examples have been set forth below for the purpose of illustration andto describe certain specific examples of the present invention of theinvention. However, the scope of this invention is not to be in any waylimited by the examples set forth herein.

Example I

H-SSZ-13 was prepared according to U.S. Pat. No. 4,544,538. Cu-SSZ-13was synthesized as following: a 2.664 g sample of Cu(OAc)₂.H₂O wasdissolved in 600 mL de-ionized water (0.022M), followed by addition ofH-SSZ-13 (10.00 g). The slurry was stirred for 2 hours at 50° C. Theblue-colored solid was collected by filtration after cooling, washedwith de-ionized water, and calcined in air at 500° C. (10° C./min) for 4hours to afford Cu-SSZ-13. Elemental analysis: Cu 3.46, Al 4.05%.

CuFe-SSZ-13 was obtained by the following procedure: 10 g of Cu-SSZ-13was suspended in a water solution of 50 mL 0.015M Fe(NO₃)₃, degassedwith N₂, and kept stirring for 2 hours at 80° C. Yellow solid wasobtained after filtration, and the filtrate was clear and colorless. Theproduct was then calcined in air at 500° C. (2° C./min) for 2 hours toyield pale yellow CuFe-SSZ-13. Elemental analysis: Cu 2.71%, Fe 0.357%,Al 3.86%.

CuFe-SSZ-13 can also be prepared by an incipient wetness method. In thismethod, 10 g of Cu-SSZ-13 was ground with 0.3 g of Fe(NO3)3.9H2O andjust enough water was added to cover the surface of Cu-SSZ-13. The colorof Cu-SSZ-13 changed slowly from green to yellow. The sample was allowedto dry in air and then calcined in air at 500° C. (2 C/min) for 4 hoursto yield pale yellow CuFe-SSZ-13.

Example II

Cu-SSZ-13 and CuFe-SSZ-13 catalyst powders were comparatively tested.The catalyst powders were mixed with equal amounts (by weight) of inertcordierite and transferred to a bench-top reactor. A de-greening wasdone in a flow of 8.5% O₂, 8% CO₂, and 7.25% H₂O with balance N₂ at atemperature of 600° C. (inlet gas temperature) and a space velocity of50,000 h⁻¹ for two hours. NO_(x) conversion efficiency experimentsemployed simulated diesel exhaust containing 8.5% O₂, 8% CO₂, 7.25% H₂O,250 ppm NO₂, 250 ppm NO, 500 ppm NH₃, and N₂ as balance at a spacevelocity of 50,000 h⁻¹ and evaluated in the temperature range of 150° C.to 650° C. Results are shown in FIG. 1. CuFe-SSZ-13 catalyst clearlyshows better performance in the 150-650° C. range. The NQ conversionperformance difference is especially noticeable at 150° C. whereCu-SSZ-13 converts ˜40% NO_(x) whereas CuFe-SSZ-13 converts ˜75% NO_(x)under test conditions.

Example III

Accelerated aging was performed on the CuFe-SSZ-13 catalyst powder byemploying an aging protocol that exposes catalyst to a temperature of675° C. for 50 hours under a flow of air containing 10% water. Testingresults are shown in FIG. 2.

CuFe-SSZ-13 catalyst demonstrates high hydrothermal durability and hashigh NO_(x) conversion performance in the 150-650° C. range. The NOxreduction at 150° C. is ˜65%, which is better than fresh Cu-SSZ-13, asshown in FIG. 1.

While there has been shown and described what are at present consideredto be examples of the invention, it will be obvious to those skilled inthe art that various changes and modifications can be prepared thereinwithout departing from the scope of the inventions defined by theappended claims.

1. A catalyst composition comprising a heterobimetallic zeolitecharacterized by a chabazite structure loaded with copper ions and atleast one trivalent metal ion other than Al³⁺, wherein said copper ionsare present in said catalyst in a loading amount of at least 1 wt % andsaid at least one trivalent metal ion other than Al³⁺ is present in saidcatalyst in a loading amount of less than 1 wt %, and said copper andtrivalent metal ion loading amounts are effective to achieve a NO_(x)conversion at 150° C. of at least 50% in the presence of an ammoniareductant.
 2. A catalyst in accordance with claim 1, wherein said atleast one trivalent metal ion comprises a trivalent transition metalion.
 3. A catalyst in accordance with claim 2, wherein said at least onetrivalent transition metal ion is selected from the group consisting ofSc³⁺, Y³⁺, V³⁺, Nb³⁺, Cr³⁺, Fe³⁺, and Co³⁺.
 4. A catalyst in accordancewith claim 1, wherein said at least one trivalent metal ion comprises atrivalent main group metal ion.
 5. A catalyst in accordance with claim4, wherein said trivalent main group metal ion is selected from thegroup consisting of Ga³⁺, In³⁺, As³⁺, Sb³⁺, and Bi³⁺.
 6. A catalyst inaccordance with claim 1, wherein said at least one trivalent metal ionis selected from the group consisting of Fe³⁺, In³⁺, Sc³⁺, La³⁺, Ce³⁺,Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, andLu³⁺.
 7. A catalyst in accordance with claim 1, wherein said at leastone trivalent metal ion comprises a combination of at least twotrivalent metal ions.
 8. A catalyst in accordance with claim 7, whereinsaid at least two trivalent metal ions comprise trivalent transitionmetal ions.
 9. A catalyst in accordance with claim 7, wherein at leastone trivalent metal ion comprises a trivalent transition metal ion andwherein at least one other trivalent metal ion comprises a trivalentlanthanide metal ion.
 10. A catalyst in accordance with claim 7, whereinat least one trivalent metal ion comprises a trivalent transition metalion and wherein at least one other trivalent metal ion comprises atrivalent main group metal ion.
 11. A catalyst in accordance with claim7, wherein at least one trivalent metal ion comprises a trivalent maingroup metal ion and wherein at least one other trivalent metal ioncomprises a trivalent lanthanide metal ion.
 12. A catalyst in accordancewith claim 1, wherein said zeolite comprises CuFe-SSZ-13.
 13. A catalystin accordance with claim 1, wherein said catalyst exhibits a NO_(x)conversion at 150° C. of at least 60%.
 14. A catalyst in accordance withclaim 13, wherein said catalyst also exhibits a NO_(x) conversion at200° C. of at least 85%.
 15. A catalyst in accordance with claim 13,wherein said catalyst also exhibits a NO_(x) conversion at 600° C. of aleast 65%.
 16. A catalytic converter comprising a catalyst loaded onto arefractory substrate, said catalyst comprising a heterobimetalliczeolite characterized by a chabazite structure loaded with copper ionsand at least one trivalent metal ion other than Al³⁺, wherein saidcopper ions are present in said catalyst in a loading amount of at least1 wt % and said at least one trivalent metal ion other than Al³⁺ ispresent in said catalyst in a loading amount of less than 1 wt %, andsaid copper and trivalent metal ion loading amounts are effective toachieve a NO_(x) conversion at 150° C. of at least 50% in the presenceof an ammonia reductant.
 17. A catalytic converter in accordance withclaim 16, wherein said at least one trivalent metal ion comprises atrivalent transition metal ion.
 18. A catalytic converter in accordancewith claim 17, wherein said trivalent transition metal ion is selectedfrom the group consisting of Sc³⁺, Y³⁺, V³⁺, Nb³⁺, Cr³⁺, Fe³⁺, and Co³⁺.19. A catalytic converter in accordance with claim 16, wherein said atleast one trivalent metal ion comprises a trivalent main group metalion.
 20. A catalytic converter in accordance with claim 19, wherein saidtrivalent main group metal ion is selected from the group consisting ofGa³⁺, In³⁺, As³⁺, Sb³⁺, and Bi³⁺.
 21. A catalytic converter inaccordance with claim 16, wherein said at least one trivalent metal ionis selected from the group consisting of Fe³⁺, In³⁺, Sc³⁺, La³⁺, Ce³⁺,Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, andLu³⁺.
 22. A catalytic converter in accordance with claim 16, whereinsaid at least one trivalent metal ion comprises a combination of atleast two trivalent metal ions.
 23. A catalytic converter in accordancewith claim 22, wherein said at least two trivalent metal ions comprisetrivalent transition metal ions.
 24. A catalytic converter in accordancewith claim 22, wherein at least one trivalent metal ion comprises atrivalent transition metal ion and wherein at least one other trivalentmetal ion comprises a trivalent lanthanide metal ion.
 25. A catalyticconverter in accordance with claim 22, wherein at least one trivalentmetal ion comprises a trivalent transition metal ion and wherein atleast one other trivalent metal ion comprises a trivalent main groupmetal ion.
 26. A catalytic converter in accordance with claim 22,wherein at least one trivalent metal ion comprises a trivalent maingroup metal ion and wherein at least one other trivalent metal ioncomprises a trivalent lanthanide metal ion.
 27. A catalytic converter inaccordance with claim 16, wherein said zeolite comprises CuFe-SSZ-13.28. A catalytic converter in accordance with claim 16, wherein saidcatalyst exhibits a NO_(x) conversion at 150° C. of at least 60%.
 29. Acatalytic converter in accordance with claim 28, wherein said catalystexhibits a NO_(x) conversion at 200° C. of at least 85%.
 30. A catalyticconverter in accordance with claim 28, wherein said catalyst exhibits aNO_(x) conversion at 600° C. of at least 65%.
 31. A catalytic converterin accordance with claim 16, wherein said refractory substrate ischaracterized by a structure selected from the group consisting of a rodstructure, a honeycomb structure, and a pinwheel structure.
 32. Thecatalyst of claim 1, wherein said copper ions are present in saidcatalyst in a loading amount of at least 1.5 wt % and said at least onetrivalent metal ion is present in said catalyst in a loading amount ofless than 1 wt %.
 33. The catalyst of claim 1, wherein said copper ionsare present in said catalyst in a loading amount of at least 2 wt % andsaid at least one trivalent metal ion is present in said catalyst in aloading amount of less than 1 wt %.